In known working cylinders without a piston rod there exists a fundamental problem, that being that the movement of the piston must be transferred to the outside of the cylinder and must be capable of being taken up there to do useful work. This is done, as shown in EP 0 147 803, in the manner that the cylinder tube is provided with a slot which extends in longitudinal direction and through which driver elements are then connected with the piston, pass through the slot and, in this way, make the movement of the piston capable of being taken up to perform work outside the cylinder. It these known prior art cylinders, however, the slot must be sealed off in a relatively complicated manner so that the inside of the cylinder is fluid-tight under pressure. Working cylinders of this kind are used, in particular, in situations in which, due to the existing operating requirements, a piston rod connected to the piston and extending outward cannot be arranged. The known art technique, however, has the disadvantage that the slot greatly reduces the torsional rigidity of the cylinder tube. Another disadvantage is that, as a result of their arrangement, a widening of the cylinder and thus of the slot is unavoidable under the action of pressure. This may result in leaks which greatly reduce the force which can be taken up by the piston.
From Federal Republic of Germany Unexamined Patent Application OS 34 03 830, a working cylinder without piston rod is known, the profiled tube of which has a closed cross section. In this known working cylinder, a slot for the arrangement of a driver between the piston and an externally guided carriage is dispensed with since, in this case, a pull belt is used which is guided outward at the ends of the cylinder tube, parallel to the inside of the cylinder, via guide rollers. This known working cylinder has the disadvantage, however, that the inside of the cylinder is of round cross section, and therefore there is nothing supportive of the piston to secure it against twisting. As a result, moments of rotation, possible during the operation of the working cylinder, are transmitted to the pull belt so that the seals of the pull belt at the ends of the cylinder tube are subjected to strong load and thus are strongly worn. Such moments of rotation of the piston occur, in particular, when the ends of the pull belt are not arranged precisely on the piston, that is precisely aligned on an axis, thus moments of rotation may be imparted. Alternatively such rotation can also occur upon the operation of the piston at high speeds of displacement in the working cylinder.
It would therefore be greatly advantageous to provide a working cylinder without a piston rod which can operate without torsional displacement of the piston within the cylinder and therefor without displacement of the ends of the pull belt.